This invention relates to a power transmission structure of a motor assist apparatus for a vehicle, and particularly to a power transmission structure of a motor assist apparatus for a vehicle including a motor (electric motor) which is driven by electrical energy and has an electric power generating function, which motor assists the driving force of an engine driven by the combustion of fuel.
Some motor vehicles are of a type commonly called a hybrid vehicle which include an engine driven by the combustion of fuel and a motor (electric motor) which is driven by electrical energy and which has a power generating function, wherein the engine is directly connected with the motor.
This motor of the hybrid vehicle is built in a motor housing arranged between a cylinder block of an engine mounted on the vehicle and case of a transmission, and consists of a motor rotor which is fixed to a rotor installation member so as to rotate with a crank shaft of the engine and a motor stator (coil) fixed in the motor housing and corresponding to this motor rotor. Such a motor assists driving force of the engine. The motor rotor possesses the flywheel, which lets inertia force occur.
One such example of a motor assist apparatus for a vehicle is disclosed in published Japanese Application Laid-Open No. 11-78555. The motor assist apparatus for a vehicle disclosed in this application includes a motor arranged between an engine and a flywheel, a ring gear arranged in an outer circumferential section of the flywheel, and a starter motor engaged with this ring gear.
However, in this motor assist apparatus, traditionally, because a ring gear is arranged in an outer circumferential section of the flywheel, the thickness (width) of the flywheel needs to be made larger in order to allow installation of the ring gear. In other words, the flywheel must be formed with a thickness sufficient to fulfill the flywheel function and to allow installation of the ring gear. Thus, the thickness of the flywheel must be increased and accordingly, the width of the whole motor must be increased, resulting in an inconvenient increase in weight.
In addition, a ring gear located in an outer circumferential section of a flywheel restricts a layout of a starter motor. Specifically, in order for the flywheel to produce the necessary inertial force so that the rotational speed of the engine is stable during low rotational speeds, the flywheel needs the extra capacity (thickness or width) at a position that is near to the crank rotation center. Accordingly, because a radius of gyration that is easy to adjust in order to get necessary inertial force cannot be taken greatly, there is the inconvenience that the weight must be increased.
Furthermore, because a motor is arranged between an engine and a flywheel, a starter motor needs to be arranged on the transmission side. In a vehicle having front wheel drive (FF), the degree of freedom of layout increases when a starter motor is arranged on an engine side due to the arrangement of the drive shaft.
However, a starter motor interferes with a drive shaft when the starter motor is arranged on the transmission side, and then there is an inconvenience due to restrictions on layout.
In order to obviate or minimize the above inconveniences, the present invention provides a power transmission structure of a motor assist apparatus for a vehicle, including a motor housing in which a motor is disposed between a cylinder block of an engine mounted on a vehicle and a case of a transmission. The motor includes a motor rotor which mounts to a rotor installation member having a flywheel, and a motor stator disposed within the motor housing so as to correspond to this motor rotor, wherein between the rotor installation member and a crank shaft of the engine, a ring gear installation member is arranged which possesses a ring gear in an outer circumferential location thereof.
In this invention, because the ring gear installation member which possesses a ring gear in an outer circumferential location is arranged between a rotor installation member and a crank shaft of the engine, the ring gear need not have a flywheel function, and the only function is to engage with a starter motor. Accordingly, the thickness of a flywheel can be reduced, and the width of a motor housing can be shortened. In addition, because the ring gear is arranged between a crank shaft and the motor housing, a starter motor can be installed from the engine side, and in a vehicle with front wheel drive (FF), the starter motor does not completely interfere with a drive shaft. Accordingly, the degree of freedom of layout of the drive shaft, starter motor and the like increases.